Presented at 53rd Annual Epidemic Intelligence Service Conference, April 1923, 2004, Atlanta. Although teachers and other adult chaperones accompanied the students on both tours, no adult reported illness. For some diseases, the most appropriate intervention may be directed at controlling or eliminating the agent at its source. Emerg Infect Dis 2002;8:398-401. Presented at Northeast Regional Epidemic Intelligence Service Conference, March 14, 2002, New York City. The alternative hypothesis, which will be adopted if the null hypothesis proves to be implausible, is that exposure is associated with disease. A very small p-value means that the observed association occurs only rarely if the null hypothesis is true. For example, in the investigation of the outbreak of E. coli O157:H7 among visitors to a county fair, the epidemiologists were able to identify one very strong risk factor consumption of beverages with ice purchased from a vendor in zone 6. In a case-control study, the investigator asks both case-patients and a comparison group of persons without disease (controls) about their exposures. To apply this test, calculate the chi-square statistic, then look up its corresponding p-value in a table of chi-squares, such as Table 6.10. The conversations about possible exposures should be open-ended and wide-ranging, not necessarily confined to the known sources and vehicles. A line listing of 26 persons with symptoms of abdominal pain and/or diarrhea is presented below. Epidemiol Bull 2001;22(4):146. Outcomes of treated human granulocytic ehrlichiosis cases. When you roll out the solution, request feedback on the success of the change made. Alternatively, they may conduct active surveillance by telephoning or visiting the facilities to collect information on any additional cases. Reclassify each patient using the revised case definition. SEER is supported by the Surveillance Research Program (SRP) in NCI's Division of Cancer Control and Population Sciences (DCCPS). Diagnoses may be uncertain, particularly early in an investigation. For example, if investigating an epidemic of meningococcal meningitis in Bamako, the case definition might be the clinical features as described in the box with onset between January and April of this year among residents and visitors of Bamako. Figure 6.2b Outbreak of SalmonellaEnteritidis Gastroenteritis Maryland, 2003 (Epidemic Curve by 6-Hour Intervals). Based on these data and knowledge of the incubation period of hepatitis A, the period of exposure was probably in early to mid-October. This association was confirmed in the laboratory, where the outbreak subtype of the Legionnaires disease bacillus was isolated from the water in the mist machines reservoir. Similarly, to control an outbreak of influenza-like illness in a nursing home, affected residents could be cohorted, that is, put together in a separate area to prevent transmission to others. Table 6.8 Risk of Gastroenteritis By Consumption of Beef Virginia, December 2003, Proportion of cases exposed = 53 57 = 93.0% Population attributable risk percent = (49.1 11.4) 49.1 = 76.7%. Emerg Infect Dis 2002;8:101928. Its purpose is to provide a factual basis from which agencies can appropriately set priorities, plan programs, and take actions to promote and protect the public's health. Return to text. Active surveillance requires substantially more time and resources and is therefore less commonly used in emergencies. This communication usually takes two forms: Epi-X is the CDCs Web-based communications solution for public health professionals. This information forms the basis for predicting whether more or fewer cases will occur in the near future. What does she do when she goes to Luverne? The first method is likely to be used when the clinical, laboratory, environmental, and/or epidemiologic evidence so obviously supports the hypotheses that formal hypothesis testing is unnecessary. In the outbreak setting, the investigators would need to specify time and place to complete the outbreak case definition. Many agencies and organizations have strict approval processes and budgetary limits that you must follow. The preparations can be grouped into two broad categories: (a) scientific and investigative issues, and (b) management and operational issues. Case Definitions Meningococcal Disease. What are the objectives of this investigation, i.e., what are you trying to accomplish? A detailed description of statistical testing is beyond the scope of this lesson, but the following text presents some key features and formulas. A square indicates the location where the envelope was opened. An X indicates locations of people whose nasal swabs tested positive for B. anthracis. Self study modules on Tuberculosis, Module 7: Confidentiality in Tuberculosis Control: Background. Single case of disease caused by an uncommon agent (e.g., glanders, smallpox, viral hemorrhagic fever, inhalational or cutaneous anthrax) without adequate epidemiologic explanation, Unusual, atypical, genetically engineered, or antiquated strain of an agent (or antibiotic-resistance pattern), Higher morbidity and mortality in association with a common disease or syndrome or failure of such patients to respond to usual therapy, Unusual disease presentation (e.g., inhalational anthrax or pneumonic plague), Disease with an unusual geographic or seasonal distribution (e.g., tularemia in a non-endemic area, influenza in the summer), Stable endemic disease with an unexplained increase in incidence (e.g., tularemia, plague), Atypical disease transmission through aerosols, food, or water, in a mode suggesting deliberate sabotage (i.e., no other physical explanation), No illness in persons who are not exposed to common ventilation systems (have separate closed ventilation systems) when illness is seen in persons in close proximity who have a common ventilation system, Several unusual or unexplained diseases coexisting in the same patient without any other explanation, Unusual illness that affects a large, disparate population (e.g., respiratory disease in a large population may suggest exposure to an inhalational pathogen or chemical agent), Illness that is unusual (or atypical) for a given population or age group (e.g., outbreak of measles-like rash in adults), Unusual pattern of death or illness among animals (which may be unexplained or attributed to an agent of bioterrorism) that precedes or accompanies illness or death in humans, Unusual pattern of death or illness among humans (which may be unexplained or attributed to an agent of bioterrorism) that precedes or accompanies illness or death in animals, Ill persons who seek treatment at about the same time (point source with compressed epidemic curve), Similar genetic type among agents isolated from temporally or spatially distinct sources, Simultaneous clusters of similar illness in noncontiguous areas, domestic or foreign, Large number of cases of unexplained diseases or deaths. While the five steps of supervision encompass the manager's responsibilities to employees, the flip side of this is that employees have five corresponding responsibilities. When designing a case-control study, one of the most important decisions is deciding who the controls should be. We should carefully scrutinize any surveillance that threatens our intellectual privacy. Like its precursor of telephone wiretapping, it must be subjected to meaningful judicial process before it is authorized. Adapted from: Lukacs SL, Hsu V, Harper S, Handzel T, Hayslett J, Khabbaz R,,et al. The health departments first responsibility is to protect the publics health, so if appropriate control measures are known and available, they should be initiated even before an epidemiologic investigation is launched. Spot maps are useful for demonstrating cases within a geographic area, but they do not take the size of the underlying population into account. If you need specialized laboratory work such as confirmation in a reference laboratory, DNA or other chemical or biological fingerprinting, or polymerase chain reaction, you must secure a sufficient number of appropriate specimens, isolates, and other laboratory material as soon as possible. Third, summarize the clinical features using frequency distributions. 5. Assessment of an outbreak by place not only provides information on the geographic extent of a problem, but may also demonstrate clusters or patterns that provide important etiologic clues. Odds ratios. Description: Name: Michael, S; Age: 53; Phone: 555-4899; Address: 48 Valley Hill Dr., Brookville, VA; County: Columbia; Sex: Male; Race: Black; Disease: Lyme Disease; Date of Onset: 9/02/2006; Lab Confirmed? The case definition must not include the exposure or risk factor you are interested in evaluating. Environmental inspection of the fairgrounds identified lack of chlorination of the well supplying water to that zone. Similarly, late cases may represent unrelated cases, cases with long incubation periods, secondary cases, or persons exposed later than most others (for example, someone eating leftovers). Nonetheless, many investigators attempt to enroll such population-based controls through dialing of random telephone numbers in the community or through a household survey. Spend time reviewing the results of the change to make sure it's made the required impact and met the desired outcomes. The affected population had a greater proportion of persons who were black, female, young, and less likely to smoke than persons in a typical Legionnaires outbreak. Administration officials say the . The controls must not have the disease being studied, but should represent the population in which the cases occurred. For example, case definitions often miss infected people who have mild or no symptoms, because they have little reason to be tested. Considering the third criterion listed earlier, notice that almost all (53 out of 57) of the cases could be accounted for by the beef. As noted earlier, many outbreaks are brought to the attention of health authorities by concerned healthcare providers or citizens. However, in many circumstances the investigators also calculate rates (number of cases divided by the population or number of people at risk). Using the dates of onset listed below, draw an epidemic curve. Step 1. In a second study they compared restaurant exposures of case-patients and healthy restaurant patrons to identify a specific menu item, a meat and cheese sandwich. If the epidemic curve points to a narrow period of exposure, what events occurred around that time? Given recent concerns about bioterrorism, investigators should consider intentional dissemination of an infectious or chemical agent when trying to determine the cause of an outbreak. But you'll need a plan. 1. Centers for Disease Control and Prevention. Sorting out roles and responsibilities in such multi-agency investigations is critical to accomplishing the disparate objectives of the different agencies. N Engl J Med 2001;344:180714. Learn about the Anniversary. Figure 6.3 Typical Epi Curves for Different Types of Spread. You can review and change the way we collect information below. The characterization often provides clues about etiology, source, and modes of transmission that can be turned into testable hypotheses (see Step 7).
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